What percentage of the immune system is located in the gut?

The gut is home to a substantial portion of the immune system, with estimates indicating that approximately two-thirds (or 66%) of immune cells reside in this area. This significant concentration is primarily due to the gut-associated lymphoid tissue (GALT), which plays a critical role in the immune response to pathogens and in maintaining immune tolerance to harmless substances, such as food and beneficial microbes. The gut's unique environment, which is constantly exposed to various antigens and microbes, necessitates a robust immune presence to protect the body from infections while promoting a balanced immune response to non-threatening substances. This is why the option indicating that two-thirds of the immune system is located in the gut is accurate.